This blog discusses current weather, weather prediction, climate issues, and other topics

Monday, December 22, 2008

Evening Update

I will be talking about Wednesday's potential storm later, but one thing is certain...there will be serious icing conditions in a few hours. Today temperatures got above freezing in most of the region and there was considerable sun. The unplowed roads became wet and slush and tonight many will freeze. We have clear skies that will promote good radiational cooling to space. Temperatures will drop into the lower 20s for most and into the teens in the normally cooler spots (away from water, in valleys or low areas). Snow really promotes nighttime cooling since snow is an excellent radiator in the infrared (that point and the fact that snow is a good reflector of solar radiation is why most record low temperatures occur when snow is on the ground).

So tomorrow morning may be a real problem with perhaps more troublesome conditions than this morning in some locations.

I am going to look at potential for snow from the upcoming storms...and it clear we have two shots at it...Wednesday and Thursday. But tomorrow, other than icy, should be a benign day with no new accumulations.

19 comments:

Anonymous
said...

Hi Cliff, I'm glad I found this site (through Crosscut) in time for the events of the past week. I just noticed that your title for the December 1 blog was "What Winter?" -- guess we have our answer now!

Whew - thanks for the update, Cliff! Just when i was thinking my decision to stick close to the eastside this evening was overkill(i.e., instead of heading home to Seattle then back here on an early a.m. commute for work), your post confirms (for me, at least) it's best to avoid that icy stuff out there. The ice & slushy roads this morning were actually a trickier drive than last Thursday when it was snowing hard.

Planning to make a break for it tomorrow (Tues) afternoon. Will stay close to the blog for more updates. Crossing-fingers this will all start clearing out by Friday.

I just found you via The Seattle Times. I hope Santa brings you the radar thing you want for our area! Thanks for the updates, I check your blog several times a day now. I appreciate the detail you give which is far more than the daily forecast I find online! You are appreciated! :)

Walked into Kingston and back home late this afternoon. The walking became treacherous as everything started to freeze up. I slipped and fell twice. Its worse on my side street hill where they plowed. Definitely boots with some sort of cleat or chains are the way to go.

Noticed that many of the drivers were going way too fast for these conditions - and several were spinning wheels and fishtailing. I wish there was a safer way into town for me except the highway.

I called Kitsap Transit and asked them if any of the buses were running. They said no. But then I saw one while in Kingston!

Can you clarify why being a good IR radiator makes temperatures drop? For this to work does the snow need to be colder than the air? Or is the snow itself actually cooling down (toward absolute zero) by radiating toward outer space? Is there some lower temperature limit below which this effect ceases, that is, at which snow is no longer a good radiator?

If snow is a good radiator of IR, wouldn't it also be a good absorber, and if so, why doesn't it melt faster in the sun? Is it because the winter sunlight doesn't contain much IR?

This past storm did not deliver as much snow to the Cascades as was expected. I am at 3500' a few miles East of the Cascade crest between Snoqualmie and Stevens Passes and barely got a foot in the past few days. Do you think this next series will deliver more snow to the mountains?

Cliff, In your editorial today you said:"But the economic loss of allowing the city to be crippled by such modest snows is substantial..." With all due respect for your facility with computer models, this point of view indicates little understanding of how the human need to increase infrastructure has caused the environmental mess now facing the planet. A minor decrease in economic activity caused by atypically persistent snow is not something that needs to be solved with inputs of money and carbon. Decreasing the rate of environmental degradation (including decreasing carbon emissions) is going to require a change of mindset and less concern for how one's city compares with New York.

Thanks, Jeff, at 6:23 near the end of the previous post. We are all responsible. One thing that has been missing in all of the criticisms is individual responsibility...being prepared. And have the critics forgotten the challenge of the hills in the region? We lived in the Chicago area; it was cold, cold, but I didn’t see any hills there on the way to work. No hills in Manhattan the last time I was there. I live in Bellevue in the Crossroads area; there was more than a foot of snow and lots of hills from here to there. Like Jeff, we drive Subaru, and it gets us out and about; the impediment is people attempting to navigate hills or go places that their vehicles are not equipped to go. That goes for the charter buses that slid down the cobble stone street in Seattle.

It is a fact; we don’t have much experience with snow driving, nor do shopping centers and businesses have much experience or the equipment for removing a foot of snow. On the other hand, the cross country skiers and the kids are taking it all in stride; sledding and skiing in local parks.

Thanks, Cliff, for giving a heads up on what may be coming and an explanation for what has happened or turned out differently than predicted. I am especially fond of your weather lore, both technical and historical.

Great info, Cliff. I haven't seen anything like these conditions in a while now, but having grown up in the midwest, I am well-trained for it. Of course, the Subaru all-wheel-drive is very forgiving. We're celebrating the holidays a little late this year when the family can get up from Portland in a few days. Still digging out in Olympia...

Hmmm...so tomorrow (Tuesday) I need to get from north Seattle (Wedgwood) to the Fauntleroy ferry dock in West Seattle, by bus. Any idea about whether it might be better to go in the morning (when it still may be icy) or in the early afternoon (risking another snow shower and even more fatigued bus drivers)? When will conditions be better?

@taobenli: I live one mile from the Fauntleroy ferry terminal. travel hear by vehicle is dicey at best. It will depend on the city being able to clean the roads of snow. The arterials here still have a lot. The busses seem to be operating mostly in shuttle loops. They are very infrequent. try to get here before the evening rush hour (today that started at three) Plan on three hours of travel and hope for one. aim for the Alaska junction on a 54, if one of the other buses are headed there, take it and transfer when you get there. The ferries are running just fine. Vashon will be a mess though too.

35 degrees in Lake Forest Park. A walk this evening with my dog and what a crunchy, icy, slippery trek. I lived in So Cal for the first part of my life and have been here for some time. Love the seasons, the weather, and now am enjoying the snow. LFP has plows and sanders and they are doing an excellent job of trying to keep the roads passable - it's a tremendous amount of work - but the weather is keeping ahead of them. Cliff's forecast last week helped me and my neighbors to get prepared. Thanks again Cliff.

IR (infrared -- also called longwave radiation) radiation is essentially heat. Things that radiate IR well basically allow them to cool quicker by being effective emitters of radiation (heat) to space. Good IR emitters are, as you suggest, usually good IR absorbers but sunlight is mostly visible radiation (aka longwave radiation).

@Walter: Snow and ice are odd materials. They have a very high reflectance in the visible (i.e. they appear white in visible light) and a very high emissivity in thermal IR (they appear black in thermal IR).

A lot of the radiation we get from the sun is in visible and short IR region (not as thermal IR). The snow does a good job of reflecting this so it doesn't heat up. It does absorbe the thermal IR (but theres not so much of that).

An object that's black in the visible (say soil) will aborb visible light, heat up then the higher temperature causes it to reradiate more in the thermal IR region. That's how a lot of stuff warms up in the sun.

The same explaination applies to the mechanism of greenhouse effect: visible and short IR in from the sun hits the surface and warms it. The surface then reradiates thermal IR which is absorbed by greenhouse gasses (e.g. water, CO2, methane and so on) then reradiated in all directions.

With snow/ice on the ground (a good thermal IR radiator) and now water vapor in the air the surfaces looses a lot of heat to space and temps drop.

“Water, ice, and snow generally have a high emissivity, 0.94 to 0.99, across the thermal infrared region. Snow is unusual in that it has a high reflectance in the solar (visible) region where most of the downwelling energy is during the day, and a very high emissivity in the thermal region.”